Warm-working of austenitic stainless steel

Abstract

A process for warm-working a forged austenitic stainless steel workpiece to improve its mechanical and physical properties is disclosed. The workpiece is subjected to a force great enough to cause deformation while the surface temperature of the workpiece is elevated in the range of above about 200° F. (95° C.) to below the lower critical temperature. The purpose of using elevated temperatures is to reduce the force required to deform the workpiece. Stabilized austenitic stainless steel can be warm-worked and still maintain its corrosion-resistant properties. The advantages of warm-working over cold-working to achieve properties are reduction of noise and improved metallurgical control.

I claim: 
     
       1. A process for developing the mechanical and physical properties of an austenitic stainless steel workpiece, the process comprising the steps of: (1) hot working the workpiece;   (2) continuously cooling the workpiece from its hot working temperature to a temperature below 200° F. (95° C.); and   (3) warm working the workpiece by subjecting it to a force sufficient to achieve said properties during said continuously cooling step while the workpiece has a surface temperature in the range above 200° F. (95° C.) and below the lower critical temperature, with both said hot working and warm working steps being carried out in a single heating cycle.   
     
     
       2. The process as claimed in claim 1 wherein subjecting the workpiece to said force comprises progressively moving the workpiece by steps through a pair of dies, the dies having a die width, each step being approximately the length of the die width, and working the workpiece between the dies at each step. 
     
     
       3. The process as claimed in claim 2 wherein the workpiece has a long dimension and a cross-sectional shape perpendicular to the long dimension and the workpiece is rotated a predetermined amount about its long dimension at each step to a position whereby the workpiece is subjected to sufficient force to correct any distortion in the cross-sectional shape caused by the previous working step. 
     
     
       4. The process as claimed in claim 12 wherein the cross-sectional shape is circular. 
     
     
       5. The process as claimed in claim 1 wherein the surface temperature of the workpiece ranges between 850° to 1200° F. (455° to 650° C.). 
     
     
       6. The process as claimed in claim 1 wherein the austenitic stainless steel is Type 321 and remains corrosion-resistant after warm-working. 
     
     
       7. A process of warm-working for developing the mechanical and physical properties of an austenitic stainless steel workpiece, the workpiece having a long dimension and a cross-sectional shape perpendicular to the long dimension, the process comprising the steps of: (1) hot working the workpiece;   (2) continuously cooling the workpiece from its hot working temperature to a temperature below 200° F. (95° C.);   (3) warm working the workpiece by progressively moving the workpiece along its long dimension during said continuously cooling step by steps through a pair of dies, with the respective dies having substantially equal widths on an open forging press, each step being approximately the length of the die width;   (4) at each step:   (a) Squeezing the workpiece at a first position;   (b) rotating the workpiece a predetermined amount about its long dimension to a second position; and   (c) squeezing the workpiece between the dies when said workpiece is in said second position;   (5) carrying out steps (3) and (4) while the surface temperature of the workpiece is between 850° and 1250° Fahrenheit (455°l  to 650° C.); and   (6) carrying out steps (1), (3) and (4) during a single heating cycle.   
     
     
       8. A process as claimed in claim 7 wherein the austenitic stainless steel is Type 321.